INTRODUCTION: Cerebellitis is an acute syndrome characterized by inflammation of the cerebellum secondary to infections or vaccinations. Involvement of one hemisphere, hemicerebellitis, is rare. The aim of this study is to describe the clinical and imaging features and outcome of three patients with hemicerebellitis.

METHODS: The clinical charts of patients with hemicerebellitis were reviewed.                                                                       

RESULTS: The patients presented with acute intense headache (2 occipital, 1 frontal) without a history of infection or vaccination. On physical examination only one patient was symptomatic showing diplopia and gait disturbance. In all patients CT scan showed hypodensity in one cerebellar hemisphere (with mass effect in one). Brain MRI revealed hemicerebellar hyperintensity on T2 and  FLAIR with gadolinium enhancement. The following studies were normal: MR angiography of the brain and neck vessels, collagen disease test, thyroid profile, hemostasis and neurometabolic testing, echocardiography, and CSF cytochemistry. Opening pressure of CSF was normal. Only one patient had positive IgM antibodies to mycoplasm. Response to pulse methylprednisolone was good in all cases. The patients remained asymptomatic on subsequent control visits. Neuroimaging at 6 months after onset showed sulcal widening in two patients.

CONCLUSIONS: The presentation of acute intense headache and scarce or absent cerebellar symptoms without any other signs of intracranial hypertension was remarkable. Hemicerebellitis is a self-limiting entity which generally has a good prognosis, however, given the risk of potentially lethal complications (brain herniation) careful clinical and imaging follow-up is warranted during the acute phase of the disease.